1. FIELD OF INVENTION
The present invention relates to radio Multiple Input Multiple Output (MIMO) communication system, and particularly to method of multiuser (MU) precoding and scheduling, which can generate multiuser precoding matrix and scheduling scheme for multiuser precoding and scheduling by using channel state information (CSI, which may be inaccurate due to various factors such as feedback quantization, feedback delay and the like) and statistic properties of CSI error fed back from a user side.
2. DESCRIPTION OF PRIOR ART
Recently, MU-MIMO has attracted much attention due to its advantage in capacity as well as the ability to work with single-antenna users (SU) and still maintain MIMO advantages.
Compared with SU-MIMO, the transmission processing of MU-MIMO is complicated due to the fact that each user must decode its messages independently without joint operation with other users. The core problem is how to solve co-channel interference (CCI) among users.
To solve this problem, multiuser precoding techniques are used in the MU-MIMO system to control or totally avoid CCI among users, so that each user suffers no or only limited interference from other users. For a total avoidance or effective control of CCI, full CSI for all users is required at the transmitter, which is only an assumption impractical to actual systems. In practice, full CSI is difficult to be achieved, and thus imperfect CSI is always used at the transmitter. With such imperfect CSI, the CCI among users cannot be totally avoided even using zero-forcing-type precoding algorithms. The residual CCI due to imperfect CSI cannot be suppressed at the receiver by common interference-suppression methods such as maximum-likelihood (ML) or minimum-mean-square-error (MMSE) detection. As a result, the CCI can only be regarded as additive noise whose average power grows with an increase in the total transmission power. This characteristic of the CCI restricts significantly the performance of MU-MIMO, especially at high SNRs.